Variable displacement pump



May 17, 1960 H. W. VAN GERPEN VARIABLE DISPLACEMENT PUMP Filed Jan. 20,1958 FIG.

H.W.VAN GERPEN United States .PatentO "ice 2,936,712 VARIABLEDISPLACEMENT PUMP Harlan W. Van Gerpen, Waterloo, Iowa, assignor, by

me sne assignments, to Deere 8: Company, a corporation of DelawareApplication January 20, 1955, Serial No. 110,119

' 7 Claims. cl'. 103-3 This invention relates "to a variabledisplacement pump and more particularly to pilot-pressure control meansfor regulating the stroke of the pump and therefore for incurringvariations in pump output. I 'Although variable displacement pumps withmeans for varying pump output are known, most of these operate on theprinciple of varying the eccentricity of the driving member relative toradial pistons, for example, while others use various types of means forpressurizing the pump itself so as to regulate the stroke of thepistons. According to the present invention, a pilot-pressure controlregulating means is afforded which acts on variablelength pistonassemblies by introducing fluid to and withdrawing fluid from thecomponents of the assemblies so that, although one component of eachassembly may be driven on a fixed stroke, the other component isregulated as to stroke length. It is a feature of the invention toprovide a pump having a plurality of variable-length piston assemblies.in which drive and pumping pistons in each assembly are constructed toafford a fluid-receiving chamber therebetween, together with manifoldmeans interconnecting the chambers of all piston assemblies so that thefluid in the manifold means and chambers may circulate from one chamberto another'as the piston assemblies are consecutively operated.Superimposed on this is means for varying the fluid in the manifold soas to incur variations in the intake strokes of the pumping parts of thepiston assemblies. This arrangement enables full-time contact betweenthe driving means and the 'drive pistons, thus eliminating noise, wear,etc. The invention features piston-control port means operative betweenthe manifold outlet and the associated chamber for trapping a cushioningamount of'fluid between the pistons so as to prevent directpistonto-piston contact. It is another object of the invention toprovide each variable-length piston assemblyas a pumping piston havingatubular skirt which telescopically receives the associated drive piston,together with controlled passage and port means for controlling theconduction of fluid to and from the chamber formed within the skirtportion of the pumping piston.

The foregoing and other important objects and desirable featuresinherent in and encompassed by the invention will become apparent as apreferred embodiment thereof is. disclosed in detail in the ensuingspecification and accompanying sheet of drawings, the several figures ofwhich are described immediately below.

Fig. 1 is a schematic view partly in section, showing the improved pumpassembly in circuit with hydraulic mechanism including a pair of fluidmotors.

Figs. 2, 3 and 4 are enlargedsectional views showing various stages inthe operation of the pump as respects one of the plurality of variablelengthpiston assemblies.

The pump selected for purposes of illustration comprises pump housing 10having a plurality of cylinders, here a pair of diametricallyopposedcylinders .12 and 14 respectively having outer ends 16 and 18. Thecylinder end 16 is connected at one side to-an intake passage 2,936,712Patented May 17, 1960 2 20 and at its other side to a discharge passage22. The cylinder end 18 is similarly connected to intake and dischargepassages 24 and 26 respectively. The intake passages 20 and 24 areconnected in common to an intake line 28 leading to reservoir at 30. Thedischarge passages 22 and 26 are connected in common to a high pressureline 32.

The pump cylinders 12 and 14 respectively carry variable-length pistonassemblies 34 and 36 which are reciprocated consecutively by drivemeans, here taking in the form of a crankshaft 38 having fixed theretoan eccentric 40. It should be noted at this point that this is ingeneral merely representative of many arrangements that the pump couldtake.

The hydraulic system to which the pump is connected by the high pressureline 32 and a high pressure branch 42 embodies a two-way fluid motor 44and a one-way fluid motor 46. The motor 44 is under control of a controlvalve illustrated schematically at 48, and a control valve for the motor46 is illustrated schematically at.50. Flow control valves at 52 and 54respectively are embodied in the high pressure line 32 and high pressure branch 42 for obvious purposes. The valves 48 and 50 may bemanually and/or servo operated, as suggested schematically at 56 and 58respectively. Both control valves are shown in their neutral positionsand are of the closed center type. The valve 48 is connected by motorlines 60' to the motor 44, and the valve 50 is connected to the motor 46via a motor line 62, a return line 64 and a supply line 66, the latterincorporating a non-return valve 68 of conventional construction andillustrated schematically here.

, As will be brought out below, the output of the pump varies accordingto the demand of the hydraulic system in response to a signal given bythe system through the medium of demand valve means 70 and various pilotpressure lines to be presently described. The valve means 70 comprises-abore 72 separated by a piston valve 74 into pilot and pressure chambers76 and 78 respectively. The pressure chamber 78 is connected to the highpressure'line 32 by a supply line 80. Pressure against the {demand valvepiston 74 via 8078 is opposed by a relatively strong spring 82, pluspilot pressure supplied to the pilot chamber 76 by a pilot line 84having. branches 86 connected respectively to the motor lines 60 and abranch 88 connected to the supply line 66 between the valve 50 and themotor 46. The pilot line branches 86 incorporate individual non-returnvalves 90, and a similar non-return valve 92 is incorporated in thepilot line branch 88. These valves may be of any c onventional type andare therefor illustrated schematlcally. The purpose of these valves isto prevent reverse flow from one pilot branch to the-other.

The demand valve piston 74 controls a port 94 which 1s connected at 96to pilot pressure manifold means '98 having outlets 100 and 102 to thecylinders 12 and 14, respectively, independently of the intake anddischarge passages 20, 22, 24 and 26. The port 94 and consequently themanifold means 98 is connected to reservoir via a line 104 having arestricted orifice 106 therein.

thevariable-lngth pistonassemblies 34 and 36, it will be seen that theoutput of the pump is controlled by the 'demand valve means 70responsive to the demand of the hydraulic system in the followingmanner: when both control valves 48 and 50 are closed, there is nopressure in the pilot line 84, since fluid trapped therein and in thepilot chamber 76 will bleed to reservoir throughthe orifice 112.--Consequently, the only force opposing the piston 74 is the spring 82,and pressure inthe high pressure line 32 and supply line 80 will balanceagainst the spring 82 so as to open the port 94 to afford a small steadyflow to the pilot line or manifold 98. Suffice it for the moment to notethat this flow and pressure are sutficient .to minimize the intakestrokes of the piston assemblies, so that the output of the pump isrelatively low, suflicient only to maintain the flow just described.When the valve 48, for example, is opened or moved to one or the otherof its active positions, pressure in the line 3280 will drop, and thespring 82 will close the demand valve piston 74 on the port 94, with theresult that fluid in the pilot manifold 98 will bleed to reservoir via96104 and the orifice 106. This, in a manner to be brought out below,will bring about an increase of the strokes of the piston assemblies 34and 36, with the result that the output in the line 32 will increaseuntil the pressure is high enough to overcome the resistance encounteredby the motor 44. As pressure builds up in one or the other of the motorlines 60, flow begins in the pilot line via whichever branch 86 isconnected to the pressurized motor line 60, and this pressure builds upbelow the demand valve piston 74 to act with the spring 82 against thepiston 74. However, because of the metering effect across the controlvalve 48, the resulting pressure drop means that the pressure at 78 willbe higher than the pilot pressure combined with the force of the spring82, as long as the motor 44 is moving, whereupon the port 94 will openand fluid will be supplied to the pilot manifold 98 to again reduce thestroke of the pump and therefore to reduce its output. When the motor 44encounters increased resistance, flow stops and pressure builds up, inthe pilot line to again close the demand valve and thereby to cut offsupply of fluid to the pilot manifold 98 with the result that the outputof the pump is increased as the strokes of the piston assemblies 34 and36 are increased. The particular demand valve means forms no part of thepresent invention and any other signal system or feedback arrangementcould be used. That illustrated forms the subject matter of ass-igneesPatent Number 2,892,312, issued June 30, 1959.

As best shown in Figs. 2, 3 and 4, each variable-length piston assemblycomprises an outer pumping piston 114 and an inner drive piston 116.Since the components of the piston assembly 36 are the same as those ofthe assembly 34, only the assembly 34 will be described.

In the particular form of the invention illustrated, the pumping piston114 has thereon a tubular skirt 118 which telescopically receives thedrive piston 116 soas to afford between the pistons a fluid chamber 120.The pumping piston is constantly opposed by biasing means in the form ofa compression spring 122 so that thepumping piston is constantly urgedin the direction of its intake stroke or downwardly or toward the drivemeans 3840. The drive piston 116 is in constant contact with theeccentric 40 of the drive means and is positively moved on an out strokeas the eccentric moves from the position of Fig. 2 to that of Fig. 4. I

The skirt 11.8 of the pumping piston has therein an aperture .124 whichremains in communication with the outlet 1% throughout the range ofmovement of the pumping piston. The interior radial face of the pumping130, an axial passage 132, and a second cross passage 134 intersectingthe axial passage 132 above a springloaded check valve 136 in said axialpassage.

Looking now at Fig. 2 and assuming that there is little or no fluid inthe manifold 98, it will be seen that the piston assembly 34 iscollapsed or relatively short, because its length is compressed betweenthe spring 122 and the drive'means 38-40.

One feature of the arrangement as shown in Fig. 2 is that a cushioningamount of fluid is trapped'in the chamber 120 between the two pistons114and 116. As will be seen, the cross passage 134 is out of register atthis time with the skirt aperture 124 and, since the check valve 136closes the intersection of the axial passage 132 and the other crosspassage 130, the fluid in the chamber cannot escape. It should be notedalso that the projections are slightly out of contact with the top faceof the drive piston 116. This trapped volume of fluid preventspiston-to-piston contact. Of course, if there is any vleakagein thesystem, as between the passage 134 and the aperture 124, the projections126 will contact the top face of the piston 116 and will maintain aslight space between the two pistons so as to improve the ability of thechamber to receive fluid.

Considering again the assumption that there is no fluid pressure in theline 98, the only fluid in the chamber 120 will be that trapped by thenon-register of the passage 134 and aperture 124. The piston 114 is thenat the end of its intake stroke, having taken in a maximum quantity offluid at the cylinder end 16 so that when the drive means 38-40 turns tothe position of Fig. 4, fluid is expelled past the check valve in thedischarge line 22. Simultaneously, the components of the other pistonassembly 36 are acting in a reverse manner; that is to say, the springfor that piston assembly is moving that pump ing piston inwardly on itsfull intake stroke. Accordingly, Fig. 2 represents what might beconsidered full stroke or maximum output of the pump. This maximumoutput will be maintainedas long as the status of fluid in the manifold98 ismaintained.

During normal or standby operation, as previously described, output ofthe pump is based only on an amount of pressure sufficient to balancethe demand valve piston 74 against the spring 82. Therefore, it isdesirable that the output of the pump be considerably reduced. This isachieved by introducing fluid to the line 98 so as to extend the lengthsof the piston assemblies 34 and 36. This occurs Via the pilot manifold98 which, as previously described, is connected to the piston assemblychambers at the outlets 1G0 and 102v Fig. 3represents a condition inwhich maximum volumehas been supplied, tothe chamber 120 with theeccentric 40 in its down position. The result of the introduction offluid to the chamber 120 via the cross passages 134 and 130 (see Fig.2)pushesthe pumping piston 114 outwardly to its maximum outward positionwhile the drive piston 116 is at its maximum in stroke position. Itshould be appreciated, of course, that the rapidly rotating drive means38-40 causes a constant change between the two pistons 114 and 116, but,

piston 114 has thereon a plurality of axial projections 126 whichprevent face-to-fac-e contact betweenthe two pistons, thus improving thefluid-receiving statusof the the drive piston 116 starts up, acommunicating register is effected between the passage 134 and the skirtaperture 124. This apertureis still in communication with the outlet100, and fluid escapes throughthe port means just described so that theposition. of the pumping piston 114 remains substantially fixed and-theentire assembly collapses as the drive piston 116 moves outwardly.

The small steady flow to the pilot line 98 across the port 94 in thedemand valve means is calibrated relative to the orifice 106 so that forany given situation it may be assumed that the volume of fluid in theline 98 and the piston assembly chambers is constant. Hence, as onepiston assembly is moving on its out stroke, the other is moving on itsin stroke and the fluid exhausted from the chamber 120, for example, asthe Fig. 4 position is achieved, is circulated through the manifold tothe chamber in the other assembly, which is increasing as the chamber120 is decreasing.

As the volume of fluid is varied in the line 98, the ability of thepistons 114 and 116 to extend and collapse will vary. For example, avolume introduced tothe chamber 120 less than that assumed in Fig. 3,will result in a position of the pumping piston 114 somewhat below thatillustrated. Consequently, the fluid trapped in the chamber 120 will actas a column or driving connection between the two pistons and, as thestroke of the piston 116 is constant, the column of fluid will carry thepumping piston 114 from the assumed position short of that in Fig. 3 tothe maximum position of Fig. 4, discharging a comparable amount of fluidat the discharge passage 22.

Several features of the invention will be apparent from the foregoingdescription. One significant feature is the shear action as the port 134goes out of register with the port 124 to establish the cushioningvolume of oil in the chamber 120 (Fig. 2). Another feature is thecirculation or interchange of fluid from the chamber of one assembly 34to the other assembly 36 via the pilot manifold 98, plus means forvarying the volume in the line 98 so as to achieve variations in thestrokes of the pumping pistons 114'Wi1iCh of course results invariations in output of the pump. Features in addition to those alreadyenumerated will readily occur to those versed in the art, as willvariations in the preferred embodiment disclosed, all of which may beachieved without departure from the spirit and scope of the invention.

What is claimed is: I p

1. A variable displacement pump, comprising: a pump housing havingintake and exhaust passages and a plurality of cylinders each connectedat one end to said passages; a plurality of drive pistons, one in eachcylinder and movable toward and away from said cylinder end respectivelyon out and in strokes of'fixed length; drive 7 infinitelyvariable-volume fluid chamber between said two associated pistons; afluid pressure manifold means having outlets leading to the chambers forincurring circulation of fluid among the chambers as the drive pistonsmove consecutively on their out strokes and as the pumping pistons arebiased on their return strokes so that a given volume of fluid trappedin the manifold means and chambers will produce a given length of travelof the pumping pistons on their intake and discharge strokes; andvolume-regulatingmeans connected to said manifold and chambers fortrapping fluid therein to effectuate said drive connections, said meansincludingan adjustable element and an associated fluid port forselectively causing increase and decrease in the volume of trapped fluidto vary the length of travel of the pumping pistons on their intake anddischarge strokes.

2. The invention defined in claim 1, including-pistoncontrolled portmeans ateach outlet operative to cut off manifold from the chamberbetween associated pistons and thus trap a cushioning amount'of fluidbetween the two' associated drive and pumping pistons to preventcomplete exhaustion of the associated chamber and there; by to preventpiston-to-piston contact between said associated pistons.

3. The invention defined in claim 1, in which: each pumping. piston hasa face portiontransverse to its axis and facing its associated drivepiston and said drive piston has a face portion transverse to its axisand facing the face on said pumping piston, said faces defining oppositeends of the associated chamber, and one of said faces has an axialprojection preventing face-to-face contact between said two pistons.

4. The invention defined in claim 1, in which: each drive piston has apassage therein leading to the associated chamber and registrable withthe associated outlet for carrying fluid to and from the chamber, andsaid piston passage and outlet are so arranged as to go out .of registerupon predetermined movement of said drive piston so as to cut off thechamber from the'manifold and thus to trap fluid in said chamber as acushion preventing direct piston-to-piston contact. 1

5. The invention defined in claim 1, in which: each pumping pistonincludes a coaxial tubular skirt extending toward and telescopicallyreceiving the associated drive piston, and the associated chamber isafforded within said skirt and between said pistons, said skirt havingan aperture therethrough for register with the associated outlet.

6. The invention defined in claim 5, in which: said aperture is soconstructed as to retain communication with said outlet throughout thefull stroke of the pumping piston; the associated drive piston has apassage therein leading atone end to the chamber and registrable at itsother. end with the skirt aperture; and said passage other end and saidaperture so arranged as to go out of register upon predeterminedmovement of said drive piston so as to trap fluid in said chamber as acushion preventing direct piston-to-piston contact.

7. The invention defined in claim 1, in which: each drive piston has afirst cross passage therein opening to the associated outlet, an axialpassage extending from said cross passage to the chamber between theassociated pistons, a check valve operative on the axial passage toprevent return flow from the axial passage to the cross passage, asecond cross passage leading to the axial passage beyond the check valveand opening to the associated outlet, and said second cross passage andoutlet being so arranged as to go out of register upon predeterminedmovement of said drive piston so as to trap fluid in said chamber as acushion preventing direct piston-to-piston contact.

References Cited in the fileof this patent UNITED STATES PATENTS FranceOct. 29, 1956

